Traffic monitoring and control system



Feb. 22, 1966 J. L. BARKER 3,237,154

TRAFFIC MONITORING AND CONTROL SYSTEM Filed Feb. 5, 1959 v 3 Sheets-Sheet 1 FIG. I

W s w I, 25 ru \L 22 l n DELAY AHEAD Z9 TAKE Tms EX\T 1 oouo'r ENTER 26 EXPRESSWAY k 32 CONGESTED I l x 2.4- r if 3| Mouu'oRlNG AND CONTROL (ENTER 23 F l G. 4 *6 i v. as L 4. i

20 l 20 -o' NORMAL ALARM 10 50 now, 400% m0 5 m LMT 1 5 smmer: 5 @AO -|oo-. new mu-nan 23F: RESET ALARM 0F cum 0 ME How/RELEASE O o: mwm; RESET f DELAY SELECTOR LL- E2551- 4% 5'7 ;75 4? VOLUME COMPUTER SPEED COMPUTER HANGE m /o/MINUTE LOCAT\ON ,CHANGE m MPH /MINUTE FOR FULL. SCALE ON BOUND LANE g FOR FULL SCALE ON MET ER METER *b- ,2 FIG 5 INVENTOR.

JOHN L. BARKER wadfl a ATTORNEY Feb. 22, 1966 J. L. BARKER 3,237,154

TRAFFIC MONITORING AND CONTROL SYSTEM Filed Feb. 5, 1959 Sheets-Sheet 2 SPEED SIGNAL (PULSE) SPEED I34 TO SPEED RATE E CLE SPEED AVERAGE OF CHANGE I? PASSAGE AND 32 COMPUTER 36 COMPUTER AND SPEED L VOLUME voLuME PASSAGE E E E Q S 22 g f iig SIGNAL (PULSE) VOLUME 82 RATE 33 COMPUTER 37 COMPUTER f FIG 2 a NEGATIVE CHANGE COINCIDENCE UNIT SPEED 47 (RELEASES RELAY vsL AVERAGE d I 43 WHEN BOTH INPUTS COMPUTER DIFFERENTIATING It EXCEED MINIMUM r CIRCUIT r NEGATIVE LIMITs) 3e RATE OF CHANGE 4| 0F SPEED E FROM voLuME 42 423 COMPUTER DIFFERENTIATING A CIRCUIT dvdt 0F $315); 2 2% I 0F VOLUME oEcREAsINg SUBSTANT| ALLY I 44 1 Y 56 Y Gs LIMIT ADJUST INSTANT TIME r 8 (DUAL) ALARM DELAY 5 46 48 I T T E HOLD/ RELEASE 62 sELEcToR itg RM s3 6 I L 66 66' POSITIVE CHANGE ARELEASE) COINCIDENCE uNIT (RELEASES RELAY VSH DELAYED WHEN BOTH INPUTS |ND|CATOR EXCEED MINIMUM POSITIVE LIMITs) 2 C E 53 (AT PRECEDING 56' EXIT RAMP) (so- 4 5 DELAY AHEAD I OUTPUT FOR BOTH LIMIT ADJUST VOLUME 8. SPEED TAKE THIS ExIT (DUAL) PA) I INCREASING f SWITCH I f2? 70 DELAI AQ EXIEES SW w ENTRANCE mgmg 72 CONGESTED RAMP OR RAMPS) 7| F INVENTOR.

I JOHN L. BARKER 27 BY E BARRIER (0R GATE) 32 532 Z[ 22 ATTORNEY Feb. 22, 1966 J. L. BARKER TRAFFIC MONITORING AND CONTROL SYSTEM 5 Sheets-Sheet 5 Filed Feb. 5, 1959 1NVENT0T." JOHN L. BARKER ATTORNEY United States Patent 3,237,154 TRAFFIC MONITORING AND CONTROL SYSTEM John L. Barker, Norwalk, C0nn., assignor, by mesne assignments, to Laboratory for Electronics, Inc., Boston, Mass., a corporationof Delaware Filed Feb. 5, 1959, Ser. No. 791,460

Claims. (Cl. 340-38) This invention relates to a system for monitoring traffic and responding to particular changes in conditions of traffic flow such as volume and speed, to indicate such changes, and to operate alarm devices and remote changeable signs, signals or other devices to guide or control trafiic in relation to entrance to and exit from highways or expressways, or to one or more of these features.

More particularly the invention relates to a system or apparatus for sensing the volume and speed of vehicular traffic on a roadway or a trafiic lane, and providing an output in response to a concurrent decrease in both volume and speed, such output being used to operate indicators or alarms to call such trafiic condition to the attention of tratlic authorities.

According to certain aspects of the invention, such output may be used directly, or after such output continues for a predetermined time, to actuate a sign or give a signal to tratfic that the slowing down condition exists ahead and also may be used to divert traffic from the roadway as by directing the traffic off an expressway to an exit ramp or otf a through street to a side or cross street to some alternate, less congested route.

From further aspects, the invention relates to electrical apparatus for determining the rate of change of traflic volume and the rate of change of traffic speed and indicating or responding to selected such changes of predetermined degree, which may be adjustable. Thus the apparatus may be arranged to respond to decreasing traffic volume alone, or to decreasing speed alone, or to increasing speed or volume, or to a combination of increasing speed and increasing volume, or to a combination of increasing speed and decreasing volume, or to a combination of decreasing speed and increasing volume, where response to or indication of such individual con ditions or combination of conditions is desired, although its principal purpose in its preferred form is in the sensing of a concurrent decrease in both speed and volume and operating indicating and control devices from such sensing. The sensing of a concurrent increase in both speed and volume is significant in resetting of alarm or control devices automatically to normal inactive condition, if desired, for example. The sensing of concurrent changes of volume and speed in opposite directions may be of significance in recognizing the approach to or the departure from some tratfic peaks for example.

In its preferred form, the present apparatus senses the trafiic changes by deriving the rate of change of the average speed and/or the rate of change of the traffic volume.

Some aspects of the invention may be applicable to fields other than trafiic, as in the determination of rate of change of a varying average over an adjustable range or beyond a selectable limit or critical value.

The great increase in the volume of vehicular tratfic on streets and highways in recent years has resulted in many of such roads becoming overloaded or congested at times despite the continued building of new road facilities. In this connection, the term trafiic volume is used in its generally accepted sense of the rate of traffic flow past a given point in number of vehicles per unit of time, such as vehicles per hour for example.

Modern high type traflic road facilities such as expressways, freeways, parkways and the like, generally limit access to widely spaced entrance ramps and exit 3,237,154 Patented Feb. 22, 1966 ramps, avoid cross traffic by over-passes or under-passes, and provide multiple trafiic lanes and easy curves and are designed for heavy trafiic at relatively high speeds. Such high type highway facilities are very costly to build and are involved in the transport of essential goods and the transport of people to and from work, in many cases, as well as for pleasure.

Even in the best of such high type facilities, most or all of the roadway may be blocked in one direction by a major accident, and in periods of heavy traffic volume, a relatively small accident or minor breakdown in one lane or some local change in road or visibility conditions may so impede trafiic that the flow of traific is suddenly slowed down to a very low level and the effective capacity of the roadway is so reduced that long lines of trafiic may accumulate with large numbers of vehicles stopped or waves of stopping and starting and moving at very low speeds may move back along the line of traffic.

The accumulation of such stopped or very slow moving traffic, may extend back several miles from the obstruction before trafiic authorities are aware of the situation, and in many cases, because of hills or curves in the road, other drivers approaching the trailing end of the line of slow moving tratlic will not realize the situation until they have passed a possible exit or other alternate route.

Certain sections of the roadway may be more susceptible to such conditions than others, but in any event, it has been a serious problem to notify traflic authorities or the traflic itself, or both, of such congested trafiic conditions as soon as possible, both from the viewpoint of getting aid to accident victims promptly and from the viewpoint of expediting trafiic and diverting it if necessary as soon as possible.

ventor with Bernard J. Midlock. Such apparatus may be used as a means for determining sustained low speeds 1n certain traffic control systems as some aspects of the .present invention as appears below.

However, speed alone may also decrease with increasing traffic volume before the latter reaches a critical level approximating the practical capacity of the road. It is known to traffic authorities that if more trafiic then arrives on the road tending to exceed this critical level, the actual trafiic volume and speed will both drop sharply, and the elfective capacity will be much reduced. Environmental factors also such as weather and road conditions such as ice, snow, wet pavement or fog will often cause marked shifts in a critical level of volume or of speed.

Thus, the impedance or congestion of trafiic popularly known as a traflic jam, may arise because of an accident, road conditions, or other factors at moderate or relatively low traific volume as well as arising at times of high traffic volume, and the problem has been to identify Therefore, I have found that a more generally reliable indication of excessive traflic congestion, particularly on normally freely running traffic facilities, is in the sensing of a combination of decreasing speed and decreasing traffic volume, and particularly where such dual decrease occurs in traflic volume and traffic speed averaged over a period of time.

Thus the present invention in its preferred form relates to a method or means for sensing trafiic congestion by a combination of substantial decrease in traffic volume with decrease in traffic speed and to applications of such sensing to remote indication or alarms or to control of traffic at a distance to avoid further congestion. Since momentary or brief reduction in speed and volume may occur from normal random traffic conditions, the preferred form of the present invention computes or employs a running average of volume and of speed, and senses a concurrent predetermined rate of decrease of both averages.

With the features of the invention in mind, it will be appreciated that it may be used to warn of impending congestion and to relieve conditions on the threshold of congestion, for example, and offer traffic an alternate route not so heavily loaded or impeded.

Also, as a variation of the invention by inversion of some of the circuitry, the combination of increasing volume and increasing speed may be used to operate remote indicators or to restore traffic diversion signs to normal, instead of having such return to normal by manual reset by a traffic authority or by absence of the congestion indicating output for a predetermined continuous time period.

It is therefore an object of the invention to sense a condition of concurrent substantial changes in traffic volume and in traflic speed in the same direction of change and to provide an output in response thereto for indicating, alarm or control purposes.

It is also an object of the invention to sense concurrently decreasing trafiic volume and traffic speed for indicating, alarm or traffic control purposes.

It is a further object of the invention to sense concurrent rapidly decreasing traflic volume and traffic speed and provide an output in response to such condition.

It is an additional object to sense concurrent predetermined minimum negative values in the rates of change of traffic volume and traffic speed for indicating, alarm or control purposes.

It is another object of the invention to determine and indicate the rate of change of trafiic volume with respect to time and the rate of change of traffic speed with respect to time in relation to running averages of such volume and speed.

It is another object of the invention to sense a predetermined minimum or threshold value of rate of change of traffic volume or trafiic speed in a predetermined direction of change for indicating, alarm or control purposes.

It is a further object of the invention to provide a method or means of traific control by sensing restriction of traffic flow by sensing substantial reduction in traffic speed and/or traffic volume at a point on a roadway and to operate or control a traffic sign and/or signal to warn of and/ or to relieve such restriction.

It is a further object of this invention to provide a method or means of traflic control by sensing traflic congestion or failure of the flow characteristics along a roadway by sensing substantial reduction of traffic volume and traffic speed at a point on the roadway, and operating a sign or signal remotely located in advance of such point to warn traffic of such congestion, or to divert traffic from such roadway at an exit or entrance thereof.

It is also an object of the invention to provide a meth-, od or means for monitoring trafiic along a highway or expressway by sampling traffic speed and traflic volume at one or more points thereon, computing running averages of traffic speed and traflic volume, and determining therefrom at a remote or central monitoring point the rate of change of speed and the rate of change of volume over a scale from negative to positive values, and providing indications or alarms or both at such remote point.

"Other objects of the invention may be apparent in the following description and appended claims with reference to the accompanying drawings in which:

FIG. 1 shows a plan view of spaced sections of a roadway such as an expressway or freeway, illustrating one application of speed and vol-ume change sensing equipment for remote monitoring and control of trafiic signs and related devices.

FIG. 2, comprising the sub-figures 2a, 2b, and 2c, illustrates in block diagram form a preferred form of traffic monitoring and control system for sensing particular changes in traffic speed and volume and responding to such changes.

FIG. 3 shows in schematic form a preferred circuit diagram of a Volume and Speed Rate of Change Unit appearing in part FIG. 2b of FIG. 2 and of certain associated alarm and control products of part FIG. 2c of FIG. 2.

FIG. 4 illustrates the indicating, adjustment and control panel of a preferred form of Vol-ume and Speed Rate of Change Unit for responding to concurrently decreasing volume and speed, of the type shown in FIG. 2b and FIG. 3.

FIG. 5 shows another form of exit ramp arrangement employing detection of traffic congestion on the ramp to operate a warning sign on the expressway approaching the ramp, or other trafiic control device.

Referring now to FIG. 1, there is shown a part of an expressway or freeway of the usual divided roadway type, of which only about one half is shown for convenience of illustration. The outer and inner edges 11 and 1 2. of the roadway for the one direction of traffic indicated by the arrow 13 extend through the three sections of roadway indicated as spaced some distance apart along the roadway by the breaks 14 and 15, introduced merely for convenience in the drawing. The central divider stnip is indicated by the edges 12 and -16, the latter edge also representing the inner edge of the companion roadway (not shown) for the opposite direction of traffic.

A detector 17 for sensing vehicle passage and speed is illustrated at the right side of the FIG. 1 at a desired point for sampling vehicular trafiic passing along the roadway in one of the [traffic lanes on the roadway. The detector 17 is illustrated over the outer lane, for example, and may be of the type known as Model RS1 Radar Speed and Impulse Unit, manufactured by Automatic Signal Division of Eastern Industries, Incooporated, the assignee of the present application for patent, and more fully described and illustrated in my copending application Serial Number 732,248, filed May 1, 1958, for Traffic Monitoring System, now US. Patent 3,059,232, issued October 16, 1962.

This speed and passage detector 17 develops an electrical signal rep-resenting passage of a vehicle and its speed in the associated trafiic lane, this signal being transmitted by a two-wire line 22, such as a telephone line, for example, to the remote monitoring and control center 23, where this signal is translated into separate channels for computing traffic volume and trafiic speed on a running average basis, and particular rates of change of speed and volume are sensed for indicating and alarm purposes and to control automatic or changeable signs or other control devices, as more fully explained later herein. The blocks within block 23 are numbered to correspond to their respective counterparts in FIGS. 2a and 2b, for example.

The monitoring and control center 23 may control via line 24 an electrically operated changeable sign 2 5, for example, in advance of exit ramp 26 to direct traffic to this exit in case of sensing traflic congestion or impending congestion at the sampling point by a combination of decreasing average speed and decreasing volume. Similarly, the center 23 may operate another changeable sign 27 via line 28 to direct traflic from entering the expressway on entrance ramp 29. A trafiic barrier or gate 32 of the remotely controlled or automatic type may be operated as a supplement to sign 27, if desired.

Other speed and passage sensing directions may be located over other lanes as indicated by such detectors 18 and 19. These may be in addition to detector 17 or one or the other may be connected to the remote center 23 instead of detector 17. If only one detector such as 17 is used, it will be in which ever lane is most representative of changes in traflic volume and speed on the roadway, particularly in case of congested traflic conditions.

For continuous monitoring on all lanes, the several detectors 17, 18 and 19 would be individually connected to the monitoring center 23 by additional channels or iines not shown, and the center 23 would have individual translating, computing and rate of change response units preferably, although their outputs might be combined for alarm control circuitry.

FIGS. 2a, 2b and 2c are arranged to be connected together, as indicated by the corresponding numbered lines .and together represent a complete traflic speed and volume sensing and concurent rates of change sensing, indicating and control system, although certain features may be omitted in some instances, as desired. For example, the sign or gate control featured on FIG. 2c may be omitted if it is desired to use the monitoring, indicating or alarm features as one aspect of the invention, as in FIGS. 2a plus 2b, or as in FIG. 2b, where average speed and volume inputs are available.

FIG. 2a shows in block diagram form the vehicle passage and speed sensing detector 17 and its connection 22 to a speed and impulse translator 31, which is preferably, but not necessarily, located in the remote monitoring and control center 23 of FIG. 1. This translator separates the combined speed and passage signal into its speed pulse or signal on line 32 and passage pulse or signal on line 33. This translator 31 is more fully disclosed in my copending application Serial Number 732,- 248, above referred to, and its details are not material to the present invention.

The speed signal pulses from individual passing vehicles are in the form of a direct current voltage substantially proportional to speed and are fed into the speed average computer 34 which is also disclosed in my said copending application, Serial Number 732,248, and provides an electr-ical voltage output on line 36 representing a running average of the latest, adjustably predetermined number of vehicles.

The volume or passage pulses for the individual vehicles are of the voltage change type, as provided by operation of a relay contact, for example, and are fed to the volume computer 35, which is also disclosed in my said copending application, Serial Number 732,248. This volume computer provides an output voltage on line 37, representative of a running average of the average number of vehicles passing the sampling point per unit of time over the latest adjustably predetermined time period, which may be of the order of several minutes, for example.

Thus the details of the components and connections of FIG. 2a are all the subject of prior patent applications,

and are illustrated here as examples of means for sensing vehicle passage and speed and providing an average speed output signal voltage and a traffic volume output Voltage which also serves as an averaged value as contrasted with an instantaneous value.

The respective output voltages representing average speed on line 36 and average volume on line 37 serve as inputs to differentiating circuits 38 and 39 respectively,

in FIG. 2b, to determine the rate of change of speed 6 as a voltage output abbreviated ds/ dt on line 41 and the date of change of volume as a voltage output abbreviated dv/dt on line 42. These rates of change are indicated on the respective meters 43 and 44, each of which is calibrated in percent between negative and positive scale limits with a center zero. Different ratios of the rate of change to the scale and to the output voltage on line 41 or on line 42 respectively may be obtained by the range adjustments indicated at 45 and 46 for the respective rate circuits. Similarly, the blocks '47 and 48 indicate resets for the respective rate circuits. These may be manually operated or by remote controlled relays, for example, to reset the rate circuits to zero, if desired.

The rate output lines 41 and 42 extend as lines 41 and 42' respectively and feed into the negative change coincidence unit 52 and may also extend into a positive change coincidence unit 53, on lines 41" and 42" as branches of lines 41' and 42' respectively.

These change response units operate as more fully disclosed in connection with the circuit diagram of FIG. 3, but serve to respond to concurrent rates of change beyond predetermined minimum limits in the stated direction, with such predetermined limits for speed and volume rates individually adjustable as indicated by the block 54 for the negative change response unit '52 and by the block 55 for the positive change response unit 53. Considering further, the negative change coincidence unit 52, it will be noted that it is indicated that this responds to concurrent negative values of rates of change of both speed and volume by releasing relay VSL to close its associated contacts to provide an output on line 56. These relay contacts are of the normally closed type, i.e., they are closed only when the relay is deenergized, but these contacts are normally held open by energization of the relay through the action of the associated circuit shown in FIG. 3, in absence of concurrent negative rates,

characterizing decreasing speed and volume, beyond the limits set by the dual individual adjustments 54.

The output line 56 is connected by a branch to an instantaneous indicator or alarm 57, and by another branch to a time delay device 58, which after a predetermined time of persistence of its input provides an output to line 60 and also via line 61 to the Hold/Release Selector 62. The output on line 60 may be used for generation of other devices, such as remotely located indicators, alarms, or trafiic warning or control signs or devices.

The hold-release selector '62, as shown more fully in FIG. 3, controls the action of the delayed alarm or indicator "63 and the associated output line 66 by determining whether the delayed alarm 63 and the output on line 66' will be maintained only as long as the concurrent negative change indicating output on line 56 continues or will be held or maintained after such indicating output on line 56 ends, as when the traffic volume and speed are no longer decreasing sufliciently.

In the hold condition, the output on line 66 and 66' and the operation of the alarm or indicator 63 is sustained until release by manual switching of this selector 62 to a release or non-hold position, or by manual operation of a remote release switch 64, or by automatic remote release via line 65, for example. Any other or remote devices which may be connected to line 66' will also be held in activated condition by the hold-release selector 62 when the latter is set to the hold condition and until released in a manner similar to that described above in relation to delayed alarm or indicator 63.

The other or remote devices may alternatively be connected to line 60, so that they will release automatically upon ending of output on line 56, and consequent reset of the time delay unit 58. The latter provides its time delay between the start of active output on line 56 and the start of output on lines 60 and 61, and after such output on line 56 has persisted for such time period, but this unit 58 is immediately resettable to terminate its output on 60, 61 if there is any interruption of output on line 56, which serves as the input to this time delay unit 58. This unit 58 acts as a slow-operate, quick release time delay relay.

The part of FIG. 2b described above corresponds in general to the circuit diagram of FIG. 3 presenting a speed and volume rate of change unit which responds to concurrent negative rates of change exceeding the limits set. There is also shown in FIG. 2b a speed and volume rate of change unit for responding to concurrent positive rates of change exceeding set limits as briefly mentioned above.

The latter unit is shown in the lower right part of 'FIG. 2b. Thus branches 41" and 42" of the rate of change output lines for speed and volume respectively extend downward to feed these outputs into a positive change coincidence unit 53. This unit 53 is the same as the corresponding negative change coincidence unit 52 above except that the diodes shown in FIG. 3 associated with the input circuits 41" and 42" would be reversed in unit 53 to respond to positive coincidence or concurrence of inputs instead of negative concurrence of inputs, and in connection with unit 53 the limits adjustment 55 for response would be set as desired for the minimum positive rates of change to which it is desired to respond.

The concurrence of positive rates of change of both volume and speed beyond the set limits releases the relay VSH in unit 53 in the same manner as concurrence of negative rates of change releases the corresponding relay VSL in unit 52. The release of relay VSH closes its contact shown in FIG. 2b to provide an output on line 70 in response to concurrence of positive rates of changes beyond the limits set by adjustor 55 and thus representing concurrent substantial increases in both traffi-c volume and speed.

This output on line 70 operates an instantaneous indicator 71 and a time delay unit 72 which, after a sufliciently long continued such output on line 70', will operate the delay indicator 73 via line 74. A further output line 65 is shown from the time delay unit 72 and serves as an automatic remote reset or release of any previously set up delayed alarm 63 or associated devices which may be held operated after initial actuation by the time delay unit 58 and the hold-release selector 62 when the latter is set to its Hold-Remote Reset position as indicated on the control panel of the assembly shown in one preferred form in FIG. 4, for example but without limitation thereto.

The two outputs 74 and 65 from time delay unit 72 are shown to illustrate both make contact and break contact operations, hence the delayed indicator 73 and other such devices would ordinarily operate from make contacts and since the reset or release through the holdrelease selector is illustrated in the circuit diagram as of the series type employing the opening at least momentarily of a normally closed contact, such as shown in the box marked remote reset in the lower right corner of FIG. 3. This contact may be of the manually operated pushbutton or momentary opened contact type or may be a break contact on the output relay of the time delay unit, represented by the designation 64 or 65. A corresponding such break contact 65 is illustrated on the output relay TL in the time delay unit 58 of FIG. 3 for example, and it will be understood that a corresponding break contact on the output relay (not shown) may be provided in time delay relay '72. It will be appreciated that electrical devices may readily be arranged to operate from either make contacts or from break contacts as desired, and the circuit arrangements are for purposes of illustration.

It will also be understood that other indicator, alarm or control devices may be connected to line 74 to be operated thereby, and that if desired to use the positive change unit 53 as an independent indication of positive change coincidence instead of for reset of the negative change coincidence alarm, the positive change unit may have a hold-release selector for control of indicator 73 or the like for example.

FIG. 20 illustrates in more detail several types of traffic control or warning devices which may be operated by one of the outputs 56', 60 or 66 derived from the output 56 of the negative change coincidence unit 52. Thus in FIG. 2c all three lines 56, 60 and 66, are shown with a switch for selecting among them for the type of control desired. The line 56' would provide instantaneous control, the line 60 would provide delayed control and the line 66' would provide delayed control subject to the action of the hold-release selector 62. The switch in FIG. 2c is shown in position connecting the latter line 66' to operate the electrical illuminated or changeable signs 25 and 27, as well as the barrier or gate 32, these reference numbers corresponding to the same devices in FIG. 1.

It will be noted in FIG. 20 that sign 27 is indicated as part of a larger sign and signal assembly, including a red or stop signal R which is operated with the sign, and a cautionary or flashing signal P operated when the sign is not operated, the operation or non-operation being under control of the relay indicated. It will be appreciated that these signs and other devices are illustrative and other forms may be used or the signals or some of the other features might be omitted in some instances.

The circuit diagram comprising FIG. 3 illustrates a preferred form of electrical apparatus corresponding to the block diagram of FIG. 2b, but illustrating particularly the upper part of FIG. 2b involving response to concurrently decreasing speed and volume and the associated alarm circuitry, without the positive change response unit 53 and its associated indicators 71 and 73 and time delay unit 72.

The positive change response unit 53 and such associated elements of FIG. 2b relate to the response to concurrently increasing speed and volume, and may be used alone in some instances or as a supplement to the concurrent decrease response part above if desired in accordance with the types of response desired for the intended use.

As mentioned above, however, if the rectifier pairs associated with input lines 41 and 42 at the left in the broken line block 52 of FIG. 3 are all reversed from the manner shown, and the relay designation VSL changed to VSH, then the part of FIG. 3 designated 52 will serve to illustrate the positive change response unit 53, it being assumed in such case that the limit or threshold adjustments 54 or 54(5) and 54(V) also will be set to the desired higher positive voltage value equivalent to a meter reading substantially above zero on its scale, which zero in turn may be equivalent to some convenient intermediate voltage value on a scale of positive voltage values of the same polarity, as positive for example in the preferred form illustrated.

Operation of the speed rate of change measuring circuit, including differentiating circuit 38, range adjust 45 and reset 47 will now be described more fully with reference to FIG. 3. It should be noted that the volume rate of change measuring circuit is an exact duplicate of the speed rate of change measuring circuit, therefore the circuitry details of the volume rate of change measuring circuit are not shown within the block 87, but the detailed circuitry above the corresponding speed rate of change measuring block 88 serves to illustrate both. The procedure of calibration and setting as will be discussed below, as well as operation of the circuitry, apply to both the speed rate of change measuring circuit and the volume rate of change measuring circuit.

Input speed information, in the form of a direct current voltage, from zero, with respect to ground, to plus volts above ground for example, is applied via lead 36, from the speed averaging computer, through a potential divid'er including resistors 101, 102, 103 and 104 to ground. The input applied via lead 36 represents the detected running average vehicle speed of the desired last number of vehicles of from zero to 100 miles per hour.

Input volume information, in the form of a direct current voltage, from zero, with respect to ground, to plus 100 volts above ground for example, is applied via lead 37 from the volume computer to a similar potential divider, not shown, in the circuitry of the volume rate of change measuring circuit 87.

The input applied via lead 37 represents the running average volume of traffic with 100 volts representing the upper end of the range of trafiic volume anticipated, for example. This may for example, be of the order of 2,000 vehicles per hour for a typical traffic lane in a roadway having free running trafiic, although some lanes might have a lower volume corresponding to the 100 volts. For convenience 100 volts are considered to equal 100% for the upper end of the desired range of trafli-c volume.

A multiposition ganged selector switch 76, including sections 76a and 76b, in conjunction with the associated resistors comprise the range adjust 45, which serves to adjust the sensitivity of the rate measuring circuit, that is, the speed change per unit of time to produce full scale reading on the rate of change meter 43.

A corresponding selector switch and associated circuitry serve as range adjust 46 for the control of sensitivity of the volume rate measuring circuit 39.

The selector switch 76 of range adjustor 45 is illustrated in FIGS. 3 and 4 in its second position, which may for example correspond to a rate of change of speed of miles per hour per minute for a 100% indication on the meter 43. The rate of change of speed may be expressed as m.p.h. per minute for example for convenience and as a reminder that this is the rate of change of the average speed and is not employed in the frequently used sense of acceleration.

The scale of values of range adjustor 45 shown in FIG.

-4 are given as one example of such values in m.p.h. change per minute, but without limitation thereto.

With range adjustor 45 so set for 10 mph. per minute the speed rate of change meter 43 will indicate minus 100% for a decrease in the running average speed of 10 'm.p.h. per minute, and will indicate plus 100% for an increase in the running average speed of 10 mph. per minute, the meter having a central zero indication for no change in speed and being linear for intermediate readings as well.

The signal from selector switch section 76a is channeled through resistor 108 to capacitor 109, the combination of which serves as a smoothing filter for the signal and to substantially eliminate any sharp changes in voltage that may occur in the signal due to any A.C. pickup or extraneous noise.

The filtered signal is fed through the differentiating network 38 including capacitor 110 and resistor 111, with the dilferentiated voltage appearing across resistor 111. Selector switch section 76b is ganged to section 76a as previously described and provides a 100% increase in the sensitivity of the unit in the maximum sensitivity or top position as compared to the second position by connection 'of resistor 112 in series with resistor 111, and resistor 112 is shunted out in all positions except the top position.

The diiferentiated input voltage, corresponding to the rate of change of the speed is applied to the grid of triode 81. Triode sections 81 and 82 are a balanced type voltmeter through which is obtained stability for accurate reading of low voltages. The meter 43 is connected via resistor 113 between the cathodes of triode sections 81 and 82. It will be noted that terminal 85 is connected to terminal 83 via line 86. This connection includes resistor 113 in the circuit between the two cathodes of the two triodes.

It may be desired to by-pass the resistor 113 via terminal 84 and to connect a recorder or remote meter between terminal 84 and terminal 83. In such case the resistance of such recorder or remote meter should approximate the value of resistor 113 which may be of the order of 2000 ohms, for example, to maintain the calibration of the unit.

The ditferentiated signal is available in voltage form at the cathode of triode 81 and is fed via line 41 and 41' to crystal rectifier 114 in the negative change coincidence unit 52.

The diiferentiating circuit 38 may be reset by operation of reset 47, which is illustrated as a pushbutton controlling contacts 118 and 119. Closure of contact 118 shunts out the input series resistance 108 in the filter network to provide a low impedance path for rapidly charging capacitors 109 and while contact 119 shunts out the resistor 111 to provide another low impedance path. The combined low impedance paths insure that capacitor 110 rapidly assumes the potential of the input voltage from the speed averaging computer as applied via line 36 as tapped by switch 76a, and thereby, upon release of the reset pushbutton 47, the unit will read the differentiated input signal from this point on.

Calibration of meter 43 is made by adjustment of two potential dividers, one potential divider including potentiometer 121 and resistor between the cathode of triode 81 and ground, the second potential divider including resistor 125 and potentiometer 126 between the DC. supply and ground. With tap 127 adjusted to its ground extremity the minus 100% rate indication is calibrated by adjustment of tap 122 on potentiometer 121. The zero or center point may then be set by adjustment of tap 127 on potentiometer 126. The latter adjustment in etfect determines the voltage about which the circuit will differentiate the input signal. Calibration of the circuit would be made with the reset button 47 held closed. After calibration is completed, the reset button 47 serves to reestablish a proper reading more quickly after any change in adjustment 45 for example or when the unit is first turned on.

The output of the differentiating circuit is biased in a positive direction with respect to ground by the potentiometer 126-127, and is applied to the grid of the cathode follower triode 81, and the output of this tube on line 41 is always positive above ground for all indications of meter 43 from minus 100% reading through zero to plus 100% reading of rate of change.

The differentiated signal on line 41 is applied via lead 41' to crystal rectifier 114 to control the impedance at junction 133 with respect to ground in cooperation with similar rectifier 114' and the limit adjust 54(s), and thus to provide a threshold control for operation of the amplifier tube 135 in response to a differentiated signal of sufficiently low positive D.C. voltage, corresponding to a sufficiently large negative rate of change of speed, as set by the threshold or limit adjuster 54(s), as more fully described below in connection with the clamping and unclamping of the input to tube 135 under control of the impedance at junction 133.

FIG. 2b illustrates in block form a limit adjust (dual) 54. This illustrates, functionally, two limit adjusting units, shown in FIG. 3: 54(s) associated with rate of and ground, and this limit adjust 54(s) serves to set the desired limit or threshold of negative rate of change of speed required for operation of the negative change coincidence unit.

To set the desired decrease as a limit on the limit ad- 'just 54(s), the potentiometer arm may be adjusted so that the positive voltage between arm 130' and ground is of the same value as the positive voltage between line 1 l 41 and ground when the meter 43 reads a value of minus for example. This setting would provide one of the two inputs required for operation of the negative change coincidence unit when a rate of decrease of 10% or more occurs in the average speed.

The negative change coincidence unit provides an indication when both the average speed decreases at a rate exceeding the preset limit as adjusted by the limit adjust 54(s) and the average volume decreases at a rate exceeding the preset limit as adjusted by the limit adjust 54(v). The individual rates of decrease, represented in a percentage, will appear on the respective meters 43 and 44, as for example minus 10%. The speed and volume rate of change signals for operation of the negative change coincidence gate are applied on lead-s 41 and 42 to rectifiers 114 and 114 and to rectifiers 115 and 115' respectively. When the positive voltage applied via lead 41' at point 133 is less than the positive voltage applied via arm 130 of limit adjust 54(s) and the positive voltage applied via lead 42 at point 133' is less than the positive voltage applied via the arm of the potentiometer of limit adjust 54(1 an unclamping of the grid 132 occurs and the negative change coincidence unit produces an output.

Operation of the clamping action at the input circuit to the negative change coincidence unit will now be explained more fully with respect to the rate of change of speed circuit, which operation is similar to that of the rate of change of volume circuit.

Sixty cycle alternating current (A.C.) of a very low value, 3 volts for example, is connected via high resistance 134 to the grid 132 of triode 135. With the negative change coincidence unit held clamped, the A.C. is prevented from acting on the grid 132 by capacitor 138, in combination with diodes 114 and 114 and/or by capacitor 137, in combination with diodes 115 and 115. With the voltage at lead 41 of a higher value than the voltage at the arm 130' of potentiometer 130, current flows through diodes 114 and 114 of sufiicient magnitude to hold the voltage at junction 133. This eflectively provides an AC. ground at junction 133 and via capacitor 138 to the grid 132.

It has been found that satisfactory operation is provided with the following typical values of components associated with the circuits producing the clamping, but without limitation to such values: resistance 134, 10 megohms; capacitor 138, l microfarad; resistance 128, 82,000 ohms; resistance 129, 3000 ohms; potentiometer 130, 3000 ohms; resistance 136, 100,000 ohms.

Resistors 128, 129 may be reduced or omitted and the value of 130 increased if desired to extend the range of adjustment. Similarly the fixed resistors in limit adjust 54(1)) may also be reduced or omitted if so desired.

Thus the output voltage, v-ia leads 41 and 42 of the rate of change of speed circuit and the rate of change of volume circuit respectively, must fall below the voltage set on the respective limit adjust circuits 54(s) and 54(v) in order that the unclamping efiect occur and thus provide a clipped AC. or a chopped DC. for amplification by the tubes 135 and 140.

This action results from the change from low impedance to high impedance at both junctions 133 and 133'. The increased impedance in the AC. circuit reduces the current and consequent voltage drop across resistor 134 and allows the AC. to act on the grid 132.

The applied 60 cycle AC. is amplified by the two high gain stages of conventional resistance capacity coupled amplifiers. The amplified AC. is then rectified at the anode circuit of triode 140 by means of diode doubler combination 141 and 142. This combination .produces a negative DC voltage (with respect to ground), which voltage is applied to the parallel connected grids of dual triode 144, which is connected to react as one tube. The applied negative voltage on the grids of dual triode 144 increases the bias of the triode to cut-off. The triode,

which is in the energizing circuit for relay VSL materially reduces the plate current and deenergizes relay VSL.

This combination of a high gain amplifier and the clamping-unclamping action described above on the AC. signal at its input and a rectified output operating the control circuit for relay VSL, provides the sensitivity required to sense the small D.C. rate signals with a high degree of accuracy at the threshold points, and to respond only beyond the desired threshold or thresholds as set by the limit adjustors.

With both inputs from 41 and 42' suflicient for unclamping, relay VSL is deenergized and closes its contacts 151 and 152 and opens its contact 153. Closure of contact 151 supplies AC. power, of the order of volts for example, to the instant alarm 57 and to output lead 56. Closure of contact 152 supplies D.C. positive power to time delay unit 58, while the opening of contact 153 opens the discharge circuit to ground for the timing capacitor 154 in the time delay unit.

The time delay unit, illustrated in the circuit diagram in FIG. 3, blocked off by a broken line boX 58 includes a timer which may, by way of example, be of the type illustrated, or may be any conventional timer or delay action relay. The timer illustrated in FIG. 3, in time delay unit 58, is one type of electronic timer that may be employed in the time delay unit. The illustrated timer is of the type disclosed and claimed by Peter C. Brockett in his copending application Serial Number 677,993, filed August 13, 1957, now US. Patent 2,964,625, under the name Electronic Timing Circuit, and assigned to the assignee of the present invention.

Normally, with relay VSL energized, contact 153 is closed and supplies a ground connection to the upper side of timing capacitor 154 to keep the capacitor substantially at ground potential. This maintains the grid in the left side of triode 170 at ground potential and keeps the left side of the triode 170 biased to cut off while the right side of triode 170 is conducting.

The switch 77 is a multiposition selector switch for selection, as desired, of one or more of the resistors 155 to 161 for inclusion in the charging circuit between the DC. supply and timing capacitor 154, to determine the timing interval.

Upon completion of the charging circuit and opening of the ground connection to the upper side of capacitor 154 and charge on the capacitor 154 is increased and the potential applied to the grid in the left side of tube is likewise increased.

When the potential applied to the grid in the left side of triode 1170 increases to an amount as determined by the setting of arm 171 on the potential divider associated with the grid in the right side of the triode 170, the left side of the triode 170 will begin to pass current and the right side of triode 170 will become nonconductive. When the left side of triode 170 becomes conductive a surge of current will pass through the coil of relay TL to energize this relay.

Energization of relay TL reverses its contacts from the normal position shown, thus providing activation of an alarm 175 and a ground connection to selector switch section 780.

Selector switch section 780 is ganged with switch section 78d in multiposition switch 78, and in its rightmost position as illustrated and in its center position, provides a ground connection for relay RS through contacts of relay TL and line 61 when relay TL is energized. Thus relay RS is energized after the time delay of unit 58, and thus in response to sustained rate of charge beyond the threshold as described above.

Energization of relay RS provides illumination of the delayed alarm 63 as well as an output via lead 66 for control of other devices. Relay RS and selector switch 78 are included in the hold/release selector 62 which is illustrated in block form in FIG. 2b and also shown on the control panel in FIG. 4. Adjustment of switch section 78d to its rightmost position provides a lock-in circuit for relay RS via its upper contact which is connected to ground through a remote reset switch 64. Adjustment of switch 78 to its center position opens the lock-in circuit for relay RS but maintains the operating circuit under control of relay TL to be operated and released directly with the latter. Adjustment of switch 78 to its leftmost position disconnects relay RS. Thus switch 78 may be changed from its rightmost position momentarily if desired for local reset.

The relay RS is provided in the preferred circuit illustrated to give greater flexibility of output control and to permit heavier duty contacts to be employed on relay RS while leaving relay TL as a lighter duty relay for example. If desired, however, the functions of these relays might be combined in relay TL by adding contacts and conventional circuitry.

Referring again to the time delay unit 58 and its control by the coincidence threshold response unit 52 as shown in FIG. 3, it will be noted that the time delay unit 58 is controlled via two input circuits from contacts of relay VSL as part of the output of unit 52. These two circuits are 56(a) from make contact 152 and 56 (b) from break contact 153. It will be appreciated that if desired the functions of these contacts in supplying D.C. for charging the time capacitor 154 and opening the discharge or reset circuit therefor could be transferred to a separate relay which might be added in unit 58 and controlled by a single lead 56 or 56'. The circuits 56(a) and 56(b) in FIG. 3 may be considered a part of control line 56 or 56' in FIG. 2b.

It will also be appreciated that the time delay unit 58 may be controlled by the circuit 56(b) from contact 153 alone if the circuit 56(a) were shunted around the contact 152 to connect directly with the DC. power supply which serves unit 58 via lead 69.

Although for convenience the DC. power supply for time delay unit 58 is drawn from. that available in unit 52 below in FIG. 3, the unit 58 may have its own power supply if desired. 1

Although the above description with reference to the circuit diagram of FIG. 3 and the block diagrams of FIG.

.2, has set forth certain preferred aspects of the invention and certain modifications of the invention, other aspects of the invention include cooperation of either of the rate of change circuits with either of the coincidence or threshold response units, as well as cooperation of both rate of change circuits with both coincidence or response units for response to rates of change of trafiic volume and traffic speed in opposite directions.

Thus while units 52 and 53 have been referred to in part above as change coincidence units, particularly in responding to concurrent conditions of changing speed and volume, it will be appreciated that either unit may serve as a threshold response unit either for the rate of change of speed alone by the omission or disconnection of the rate of change of volume unit, blocks 87 and 54(v) in FIG. 3 for example, or for the rate of change of volume unit alone by the omission or disconnection of the rate of change of speed unit blocks 88 and 54(s) in FIG. 3 for example. As an alternative, for selective operation of unit 52. from either the speed unit or the. volume unit or both, switches may be placed in the lines above and below junction 131, on either side of capacitors 137 and 138 in FIG. 3, to open or close these circuits individually as desired in unit 52. Similar provision may .be made in unit 53 if desired.

Various combinations of units include the speed rate of change unit alone cooperating either with coincidence or response unit 52 alone adjusted for response to de-. creasing speed alone or with coincidence or response unit response unit 53 alone adjusted for response to increasing volume. Other combinations for response to different concurrent conditions include both the rate of change of speed and the rate of change of volume units coopcrating with a coincidence unit such as 52 but with diodes 114 and 114 reversed from that shown in FIG. 3 and limit adjust 54(s) adjusted for response to increasing speed and diodes 115 and 115' as shown in FIG. 3 and limit adjust 54(v) adjusted for response to decreasing volume so that the output of unit 52 as modified would be in response to concurrently increasing speed and decreasing volume, or the reverse combination with diodes 114 and 114 as shown in FIG. 3 and limit adjust 54(s) adjusted to respond to decreasing speed and diodes 115 and .115 reversed as compared with FIG. 3 and limit adjust 54(v) adjusted to respond to increasing volume so that the output of unit 52 as modified would be in response to concurrently decreasing speed and increasing volume.

Thus in more general terms the circuits may be readily arranged for response to the rate of change of speed alone exceeding a predetermined amount in a predetermined direction of change, or for response to the rate of change of volume alone exceeding a predetermined amount in a predetermined direction of change, or for response to concurrent rates of speed and volume of predetermined amounts and in predetermined directions of change, which may be the same directions of opposite directions.

As previously mentioned, the limit adjusters 54 (s) and 54(v) may be individually adjusted for different 'values and over a wide range, such as to obtain coincidence response to a 10% decrease in the rate of change of speed and a 15% decrease in the rate of change of volume, with the diodes as shown in FIG. .3, for example, or a 2% increase in the rate of change of speed and a 5% decrease in the rate of change of volume, 'with diodes 114 .and 114' reversed, for example, or any other desired values.

FIG. 4 illustrates a [form of control panel that may be employed in one embodiment of the invention.

Similar electrical components that appear in part on the control panel of FIG. 4 and also in FIG. 2b and FIG. 3 are similarly labeled, as for example meters 43 and 44, range adjusters 45 and 46, limit indicator 57 and remote alarm 63 which may be an alarm itself or an indicator lamp on the panel to show when a remotely located alarm is operated. The time delay adjustment 77 and indicator lamp correspond to similarly labeled components illustrated in FIG. 3. The scale above the time delay adjuster 77 may be in minutes for example.

Certain blocks on the control panel are expanded below the face of the panel for convenience in the drawing to make the legend appearing thereon legible. Thus the legend Speed Computer Change in MPH/Minute for Full Scale on Meter refers to the scale of figures associated with the adjusting knob of the speed range adjustor 45, and the large horizontal arrow identifies the associated speed rate of change meter 43. Similarly the legend Volume Computer Change in %/Minute for Full Scale on the Meter associates the range of values of the volume range adjustor 46 above it with the volume rate of change meter to the left. The ranges of values for the several meters and adjustors serve as examples without limitation thereto.

Neither of the limit adjustors 54(s) or 54(v) comprising the limit adjust 54 appear on the control panel as shown in FIG. 4. It is anticipated that the limit adjustors 54(s) and 54(v) will be varied much less often than the adjustments that appear on the control panel, and thus may be more suitably located elsewhere in or on the apparatus, but it will be understood that such limit adjustors may be located on the control panel of FIG. 4 if desired.

FIG. illustrates another form of exit ramp from an expressway, parkway or the like, the exit ramp extending from a deceleration lane on the expressway. The arrow 13 indicates the direction of vehicle travel, as the similar arrow in FIG. 1, and the lines 11 and 12 in FIG. 5 represent the limits of one half of the expressway as in FIG. 1 above. The exit ramp 26 terminates at the intersection of a roadway indicated by lines 30 and 30. The bridge 29 indicates that the roadway 3fi30' is illustrated as passing under the expressway 11-12 for example.

The diagrammatic showing in FIG. 5 and particularly the length of the roadway 1142 and of the exit ramp 26' in FIG. 5 are condensed or foreshortened for convenience of illustration.

A vehicle speed and passage sensing unit 17, similar to the corresponding labeled detector in FIG. 1, is illustrated over the exit ramp in FIG. 5. The unit 17 would be suspended over the roadway by means of a pole and projecting arm or by means of a span wire, or other means.

Sensing unit 17 is preferably placed over the exit ramp intermediate the ends of the ramp and at least several car lengths in advance of the signal 50 so as to sense vehicles in the normally relatively free moving traffic Zone along the ramp rather than the first few cars stopping or slowing down at the entrance to the lower road 30-30 for example.

Thus the sensing unit 17 may be located generally near the middle of the length of the ramp'as shown for example, so as to sense congestion or blocking soon enough to warn approaching traffic or to clear the accumulated traflic through the lower signal or road intersection but not to be unduly affected by ordinary changes in speed or in volume occurring directly adjacent to the intersection.

The box 23' in block form, represents one or another of the forms of apparatus mentioned above for responding to decreasing speed or to concurrently decreasing speed and volume for example, as more fully discussed below.

The line 24 represents an output line through which a sign 25' would be illuminated or otherwise controlled so as to warn approaching vehicles on the deceleration lane of the condition of the exit ramp. The sign 25' is illustrated by way of example only for other signs as desired may be used in its stead or cooperatively with the sign 25'.

The line 49 represents an additional output line extending to a block 44) which block represents a controller which controls the traffic signal 50 through line 51. The trafiic signal is preferably of the usual type having red, yellow and green signal lights for the several directions, as indicated by the small arrows for example. The controller in block 50 may include one of the well known types of traffic signal controllers for operating the signal lights through a time cycle to accord right of way to the intersecting roads in sequence, and in addition will preferably include a supplemental preemptive controller for acting through or superseding the normal traffic signal controller to preempt or otherwise obtain the right of way for the exit ramp to permit the accummulated traffic on the exit ramp to be reduced or cleared into the intersection.

Several forms of preemptive control of traffic signals in connection with or superseding a traffic signal controller are illustrated in U.S. Patent 2,203,871, issued June 11, 1940, to W. R. Koch, and in U.S. Patent 2,234,606, issued March 11, 1941, to F. H. Richterkessing.

The preemptive controller may be operated by a thresh old response unit such as 52 from output line 56 for example either in response to substantially decreasing speed alone or in response to concurrently decreasing speed and volume as discussed above, or as otherwise discussed below.

The unit 23 in FIG. 5 may be of the same type as unit 23 above in FIG. 1 for example, or may employ only part of the apparatus shown in the latter. It will be understood that either of these units 23 or 23' may employ both the upper and lower parts of FIG. 2b for concurrent negative change operation response for speed and volume and for concurrent positive change release response for speed and volume, or may employ only the upper part of FIG. 212 for the negative change response without the positive change response, as well as other variations discussed above.

Although preferably the unit 23 particularly would employ response to concurrently decreasing speed and volume of traffic for control of signs or signals, either of the units 23 and 23' and particularly unit 23 in some circumstances might use decreasing speed alone as by only speed circuit 88 and limit adjust 54(s) feeding into threshold response amplifier unit 52, or might use sustained low speed below some value considered critical such as by the successive critical speed response unit of the above mentioned copending application Ser. No. 777,711 on Traffic Speed Monitor for example, for control of the signs or signal, or for operation of the preemptive cont-roller for control of the signal to accord right of way to traffic entering the road 3040' from the ramp.

The exit ramp may have other well known forms where trafiic from the ramp merges with traffic on the other road and is normally free flowing throughout wsithout traffic signal or other stop and go control. It will be understood that the exit ramp may also sweep in an are from the expressway to the right and backward from the far side of the bridge 29 in the familiar clover leaf pattern instead of in the form illustrated in FIG. 5.

It will be understood that the advance warning sign 25' alone may be employed to be operated in response to sustained low or substantially decreasing speed alone or to a combination of decreasing speed and volume, or the preemptive controller may be employed alone to be so operated, or both sign and pre-emptive controller may be employed as in the preferred form illustrated.

The wording of the signs in the several drawings is primarily for illustrative example and other wording may be found suitable in some cases until adoption of some accepted standards for such service.

It will be noted that the term negative rate of change is used to describe a rate of change in the direction of decrease. Similarly a positive rate of change is in the direction of increase.

Although a number of aspects of the invention and modifications of the form thereof have been described above, it will be understood by those skilled in the art that various other modifications might be made or rearrangements or substitution of parts and the like without departing from the spirit of the invention within the scope of the claims.

I claim:

1. A traffic monitoring and control system including:

detector means for sensing vehicle movement characteristics in a stream of traffic to obtain first and second electrical signals therefrom;

traffic flow characteristic computer means for receiving said first and second electrical signals and providing thereform third and fourth electrical voltage signals having a value proportional to the running average value of traffic movement characteristics over a period of time, these movement characteristics including traflic speed and trafiic volume represented by said movement characteristics; differentiating circuit means receiving said third and fourth electrical signals for providing electrical 17 output rate of change voltage signals which are proportional to the rate of change of said third and fourth electrical voltage signals, respectively, and represent the rate of change of said traflic flow characteristics;

biasing means for providing a reference level for said electrical output rate of change voltage signals; and,

threshold response means for providing a control sig nal output in response to said electrical output rate of change voltage signals which exceeds said reference level of said biasing means, whereby an indicator and traffic control device may be controlled by the last-named control signal outputs from the threshold response means.

2. A trafiic monitoring and control system as in claim 1 including:

indicating means coupled to said threshold response means to be operated by said output thereof;

holding means for holding said indicator means operative until released; and,

resetting means for releasing said holding means.

3. In combination, vehicle speed detecting means which senses the passage of individual vehicles and produces output vehicle speed electrical signals thereby;

vehicle passage detecting means which senses the passage of individual vehicles and produces vehicle volume electrical signals thereby;

a speed averaging computer device operated by said vehicle speed signals to produce an electrical signal representing an average traflic speed;

a volume computer device operated by the vehicle passage signals to produce an electrical signal representing traffic volume as averaged over a period of time;

differentiating circuit means receiving said average traffic speed signal to provide therefrom a speed rate of change signal,

further differentiating circuit means receiving said average traffic volume signal to provide therefrom a trafiic volume rate of change signal, each said rate of change signal having a range of values thereof between a maximum rate of decrease through zero to a maximum rate of increase,

and change coincidence response means receiving the respective traflic volume rate of change signals and traffic speed rate of change signals as inputs to provide an electrical output adapted to control a trafiic indicator in accordance with the relative values of said respective rate of change signals for traflic volume and traffic speed respectively.

4. A combination as in claim 3 in which said change coincidence response means includes means for providing said output for control of a trafiic indicator in response to concurrent rate of change signals of .t-raflic volume and trafiic speed of at least predetermined minimum amount and predetermined direction of rate of change with respect to zero rate of change.

5. A combination as in claim 3 in which change coincidence response means includes means for providing said control output in response to concurrent rate of change signals for traflic volume and trafiic speed of predetermined minimum amounts in the same direction of displacement with respect to zero rate of change.

6. A combination as in claim 3 and in which said change coincidence response means includes means for providing said control output in response to 18 concurrent rate of change signals of traific volume and traffic speed of predetermined minimum amount in a negative direction of displacement with respect to zero representative of concurrently decreasing trafiic volume and traffic speed.

7. A combination as in claim 6 and in which said change coincidence response means includes means for providing a further control output in response to concurrent rate of change signals for trafiic volume and traflic speed of predetermined minimum amount and of positive direction of displacement with respect to zero representing concurrent increase of trafiic volume and trafiic speed.

8. A combination as in claim 7 and including traflic control indicator means coupled to said change coincidence response means to be operated by the first said control output thereof in response to concurrently decreasing traflic speed and trafiic volume and to include means for holding said indicator means so operated, and means controlled by said further control output to control said holding means for releasing said indicator means from operated condition in response to concurrently increasing traflic speed and traflic volume.

9. Electrical apparatus for use with a system producing individual electrical signals having varying values representative of running averages of traffic speed :and traflic volume respectively in vehicular trafiic, said apparatus in cluding in combination,

means including difierentiating circuits for receiving said electrical signals representing average traffic speed and traffic volume as inputs respectively and producing therefrom individual further electrical signals having values representative of the rates of change of the first mentioned electrical signals respectively, each said further electrical signal value being over a range of values corresponding to a range of rates of change between a maximum rate of decrease through zero to .a maximum rate of increase, and including means for adjustably predetermining the respective further electrical signal values in relation to the corresponding rates of change of the respective first mentioned electrical signals as received, and

change coincidence response means for providing a control output in response to concurrent said further respective electrical signals of predetermined values representative of concurrent rates of change of traffic speed and volume of at least predetermined amounts and of predetermined direction of displacement with respect to zero.

10. A combination as in claim 9 and including limit adjusting means for the respective rate of change signals for trafiic volume and traflic speed for adjusting said predetermined amounts of rate of change for so providing said control output.

References Cited by the Examiner UNITED STATES PATENTS 1,406,625 2/ 1922 Duran 340-31 2,874,367 2/1959 Palma 340-31 2,891,237 6/1959 Sink 340174 2,892,995 6/1959 Kearney 34031 2,894,249 7/ 1959 Hughes 340174 2,933,716 4/1960 Soderberg 34031 NEIL C. READ, Primary Examiner.

BENNETT G. MILLER, IRVING L. SRAGOW,

Examiners. 

1. A TRAFFIC MONITORING AND CONTROL SYSTEM INCLUDING: DETECTOR MEANS FOR SENSING VEHICLE MOVEMENT CHARACTERISTICS IN A STREAM OF TRAFFIC TO OBTAIN FIRST AND SECOND ELECTRICAL SIGNALS THEREFROM; TRAFFIC FLOW CHARACTERISTIC COMPUTER MEANS FOR RECEIVING SAID FIRST AND SECOND ELECTRICAL SIGNALS AND PROVIDING THEREFORM THIRD AND FOURTH ELECTRICAL VOLTAGE SIGNALS HAVING A VALUE PROPORTIONAL TO THE RUNNING AVERAGE VALUE OF TRAFFIC MOVEMENT CHARACTERISTICS OVER A PERIOD OF TIME, THESE MOVEMENT CHARACTERISTICS INCLUDING TRAFFIC SPEED AND TRAFFIC VOLUME REPRESENTED BY SAID MOVEMENT CHARACTERISTICS; DIFFERENTIATING CIRCUIT MEANS RECEIVING SAID THIRD AND FOURTH ELECTRICAL SIGNALS FOR PROVIDING ELECTRICAL OUTPUT RATE OF CHANGE VOLTAGE SIGNALS WHICH ARE PROPORTIONAL TO THE RATE OF CHANGE OF SAID THIRD AND FOURTH ELECTRICAL VOLTAGE SIGNALS, RESPECTIVELY, AND REPRESENT THE RATE OF CHANGE O SAID TRAFFIC FLOW CHARACTERISTICS; BIASING MEANS FOR PROVIDING A REFERENCE LEVEL OF SAID ELECTRICAL OUTPUT RATE OF CHANGE VOLTAGE SIGNALS; AND, THRESHOLD RESPONSE MEANS FOR PROVIDING A CONTROL SIGNAL OUTPUT IN RESPONSE TO SAID ELECTRICAL OUTPUT RATE OF CHANGE VOLTAGE SIGNALS WHICH EXCEEDS SAID REFERENCE LEVEL OF SAID BIASING MEANS, WHEREBY AN INDICATOR AND TRAFFIC CONTROL DEVICE MAY BE CONTROLLED BY THE LAST-NAMED CONTROL SIGNAL OUTPUTS FROM THE THRESHOLD RESPONSE MEANS. 